1. Field of the Invention
The present invention relates to a method for manufacturing a pneumatic tire, and more specifically, to a method for manufacturing a pneumatic tire, the method being capable of reducing tire failure that would occur when a film made of a thermoplastic resin or a thermoplastic elastomer composition is used as an air permeation preventive layer.
2. Description of the Related Art
It has been recently proposed that a film made of a thermoplastic resin or a thermoplastic elastomer composition is disposed as an air permeation preventive layer for a pneumatic tire instead of a rubber layer made of an isobutylene-isoprene rubber, the thermoplastic elastomer composition obtained by blending an elastomer with a thermoplastic resin.
The following method for forming such air permeation preventive layer has been known. In this method, a thermoplastic resin or a thermoplastic elastomer composition is extruded and molded into a cylindrical film by inflation molding or the like. The cylindrical film thus molded is folded into a sheet shape. Then, rubber layers serving as a tie rubber are stacked respectively onto both sides of the folded film, so that a laminate is formed. Thereafter, the laminate is expanded into a cylindrical shape, and fitted onto a tire making drum, so that an uncured tire is formed. Such method is disclosed, for example, in Japanese patent application Kokai publication Nos. Hei 10-29248 and 2001-260137.
However, the stacking of rubber layers onto both surfaces of a film folded into the sheet shape has the following problems. If the rubber layers are not stacked in a manner that the rubber layers protrude from both edge portions of the film in the width direction, a portion where the edge portions of the rubber layers are spliced (hereinafter, this portion is referred to as a spliced portion) may be opened when the laminate is fitted onto a tire making drum, thus causing tire failure. However, while such too small amount of protrusion of the rubber layers may cause the spliced portion to open, too large amount of protrusion, by contrast, may cause another problem. Specifically, too large amount of protrusion causes the spliced portion to protrude to a large extent in the radius direction of the tire making drum when the laminate is fitted onto the drum. When other components of a tire are pasted on such spliced portion, an air pocket or a wrinkle is likely to be generated around the spliced portion, thus also causing tire failure. However, consider the process of stacking rubber layers each formed to have a certain width respectively on both surfaces of a film folded into the sheet shape. In this process, it is very difficult, when stacking the rubber layers, to strictly adjust the amount of protrusion of rubber from each edge portion of the film in the width direction. Such difficulty leads to reduction in productivity of tires.